(1) Field of the Invention
The present invention relates to a VC (Virtual Connection) switching method in an ATM (Asynchronous Transfer Mode) network and an ATM switch. More particularly, the invention relates to a VC switching method and an ATM switch for switching a PVC (Permanent Virtual Connection) path to an SVC (Switched Virtual Connection) path as a bypass.
(2) Description of the Related Art
In recent years, a communication system called ATM communication applicable to both data communications and real-time communications of voice and the like is being practically used. As various applications dealing with multimedia are integrated in a communication network, in order to increase the reliability of the network, it is indispensable to provide a communication node having the function of bypassing a failed line when a line failure or a device failure occurs.
An example of means of switching a failed PVC to an SVC is soft PVPC or soft PVCC disclosed in The ATM Forum Technical Committee xe2x80x9cPrivate Network-Network Interface Specification Version 1.0 (PNNI 1.0)xe2x80x9d af-pnni-0055.000, March, 1996.
In the case of switching a PVC to an SVC by using the soft PVPC or soft PVCC, all nodes (ATM switches) positioning along an end-to-end path have to be provided with a PNNI (Private Network-Network Interface) protocol, and even in a steady communication state in which there is no bypassing operation, it is necessary to execute a complicated PNNI protocol process at each of the nodes to automatically recognize a network configuration. When a node existing between the ends does not have the PNNI or a transit node positioning between the nodes does not have the PNNI, the PVC cannot be bypassed by using the SVC.
An example of a known VC switching method of switching the PVC to the SVC is disclosed in Japanese Unexamined Patent Application No. 9-266480. In the method, an ATM switch which detects a failure in a PVC line stores the relations of an address of a neighboring switch, egress port number of the neighboring switch, and egress port number of itself into a neighboring node connecting information table for PVC switching on the basis of neighboring node connecting information obtained by a routing information collecting function related to a network control. When a link failure is detected in a line interface, the ATM switch obtains the address of a neighboring switch connected to a failed egress port by referring to the neighboring node connecting information for PVC switching, selects an optimum route to the neighboring switch by a network control processing unit, and transmits a call setup message via the optimum route.
The call setup message uses the neighboring switch address as a called party address and includes VPI/VCI indicative of a PVC on the failed link and a failed port number as calling party sub-address information elements. The neighboring switch specifies the egress port number of itself connected to the failed link by referring to the neighboring node connecting information for PVC switching on the basis of the calling party address (neighboring switch address) and the failed egress port number (neighboring switch egress port number) indicated by the calling party sub-address information elements in the call setup message. The neighboring switch determines the VPI/VCI for connection to the bypass route, notifies the VPI/VCI as a call reception message to the neighboring switch at the origination side and sends a connection acknowledge message.
On receipt of the call reception message and the connection acknowledge message, the neighboring switch on the origination side executes the process of switching the failed PVC to the SVC and then transmits a notification message indicative of completion of the connection to a neighboring switch. On receipt of the notification message, the neighboring switch executes the process of switching the failed PVC to the SVC.
Another known example of switching the PVC to the SVC is disclosed in Japanese Unexamined Patent Application No. 10-32575. The publication discloses a VC switching method of, in a manner similar to the above conventional technique, forming a network topology information table by using the PNNI protocol or the like in advance, retrieving a bypass route to an ATM switch at the other party from the table when a VC switching request is generated, and transmitting a connection request message including bypass information.
The connection request message includes an ATM address of the ATM switch at the other party as a called party address. In the message, a line ID of the ATM switch at the other party and the VPI/VCI of the VC to be bypassed which are obtained from the network topology information table are set as bypass information. In this case, the ATM switch at the other party which receives the connection request message determines that the received request relates to a request for bypassing a specific VC according to the bypass information and information prepared in the ATM switch, and switches the specific VC to an alternative SVC.
Since the two conventional techniques are made on condition that each of the ATM switches has the routing information collecting function such as the PNNI to determine a bypass, they have problems which are to be solved by the present invention.
A VC switching system of preparing a standby PVC for each of PVCs which operate in a normal route and switching the PVC to the corresponding standby PVC when a failure occurs in the normal route can be considered. The switching method using the PVC as a bypass has, however, a problem such that the utilization factor of communication resources in a standby PVC line deteriorates at the time of operating the normal route.
In place of preparing the PVC as a bypass, which vainly occupies the communication resources, in order to set an SVC as necessary, a function of promptly selecting a route of an SVC as a bypass and calling the SVC when a failure in the PVC is detected or when a bypassing command is received has to be provided.
In the case where an SVC for use in a conventional call and an alternative SVC coexist in the same node, it is necessary to prepare a function of discriminating a call setup message for bypassing control from conventional call setup messages when they are received from another node and specifying a PVC to be bypassed if a plurality of PVCs exist in the node. Further, when the cause of the bypassing is resolved, a function of specifying the relation between a PVC to be recovered and an alternative SVC to switch back the VC is necessary.
An object of the invention is to solve the problems and to provide a VC switching method capable of promptly switching a PVC to an SVC.
Another object of the invention is to provide an ATM switch capable of promptly switching a PVC to an SVC without requiring a network configuration recognizing function such as the PNNI protocol.
Further another object of the invention is to provide an ATM switch capable of promptly switching the SVC back to the original PVC when the cause of bypassing is resolved.
In order to achieve the objects, according to the invention, there is provided a method of switching a virtual connection between first and second ATM switches in an ATM network, comprising the steps of: storing into each of said first and second ATM switches, (a) bypassing control information in association with PVC management information specifying a PVC between said ATM switches, the bypassing control information indicating relations of SVC specifying information for specifying an SVC to be used as a bypass of the PVC, address information of an ATM switch at the other party, and the other party PVC information for specifying the PVC in said the other party ATM switch; (b) transmitting a bypassing call setup message from said first ATM switch to a line specified by the SVC specifying information at the time of an operation of switching the PVC to the SVC, the bypassing call setup message including said the other party PVC information and using the address information of the ATM switch at the other party as a called party address; (c) switching the PVC to the SVC by said first ATM switch on the basis of the PVC management information and said the other party SVC information when a response is received from said second ATM switch; and (d) referring to the bypassing control information corresponding to said the other party PVC information included in the bypassing call setup message by said second ATM switch, thereby to switch a PVC specified by said the other party PVC information to an SVC specified by the SVC specifying information includes as a part of the referred bypassing control information.
When a plurality of PVCs are multiplexed on a physical or logical line, the PVC management information and bypassing control information is prepared for each of the PVCs. When a bypassing factor occurs in a specific physical or logical line, an ATM switch which is using the physical or logical line generates a bypassing call setup message for each of the PVCs multiplexed on the physical or logical line, and each of the plurality of PVCs is switched to an SVC.
An ATM switch according to the invention comprising: a memory for storing bypassing control information blocks in association with PVC management information blocks for each of PVCs of the ATM switch, each of said bypassing control information blocks indicating relations of SVC specifying information for specifying an SVC to be used as a bypass of the PVC, address information of an ATM switch at the other party in the PVC, and the other party PVC information for specifying the PVC in said the other party ATM switch; first means for transmitting when a bypassing factor from a specific PVC to an SVC occurs, a bypassing call setup message to a line specified by the SVC specifying information corresponding to the specific PVC and switching the PVC to the SVC on the basis of the PVC specifying information and said the other party SVC information, the bypassing call setup message including said the other party PVC information and using the address information of the ATM switch at the other party as a called party address; and second means for referring when a bypassing call setup message is received from another ATM switch, to the bypassing control information block corresponding to the PVC specifying information included in said referred bypassing call setup message and switching a PVC specified by said the other party PVC information to an SVC specified by the SVC specifying information included in the bypassing control information block.
The other objects and features of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings.